This invention relates to a technique for ascertaining the relative position of a cable within a pipe.
Providers of telecommunications service, such as ATandT, often bury their optical fiber cables underground for reasons of safety and esthetics. In many instances, a pipe, usually made from metal such as steel or the like, surrounds and protects the buried optical fiber cable from unstable soil, heavily traveled right-of-ways, and other risks that could aversely affect the cable. Typically, the pipes used for cable burial have a diameter between 3 and 12 inches and a wall thickness of xe2x85x9-xc2xc inch to provide a barrier against exposure of the cable. Unfortunately, instances do occur when access to the cable within the pipe becomes necessary, such as during cable repair. Present day methods for gaining access to a buried optical fiber cable within a pipe involves cutting the pipe with a saw or cutting torch, such as the in the case of a metallic pipe. Cutting the pipe in this manner, while effective, often causes damage to the cable itself, requiring the service provider to place the cable out-of-service and re-route traffic in advance of any such cutting rather than risk an accidental service outage.
A technician performing the cutting generally has no knowledge of the exact position of the cable within the pipe. Normally, one would expect that the cable would lie along the bottom of the pipe. However, the optical fiber cable often will twist and turn upon being pulled through the pipe during installation, causing portions of the cable to lie above the pipe bottom. Thus, the technician cutting into the top portion of a cable-containing pipe may inadvertently cut into the optical fiber cable, causing damage that will likely result in a service outage.
Thus, there is a need for a technique for detecting the relative position of a cable within a pipe.
Briefly, in accordance with a preferred embodiment of the invention, a method is provided for locating a cable within a pipe. To locate the cable, a locating signal is applied to a metallic part of the cable for radiation beyond the pipe. The strength of the radiated locating signal is measured at first and second distances from the pipe along a normal perpendicular to the longitudinal axis of the pipe. The difference between the locating signal strengths at the two distances is determined and the relative location of the cable in the pipe is established from the locating signal strength difference.